1. Field of the Invention
The present invention relates to a method of driving a liquid-drop spraying device for use in various kinds of machines for processing the above described liquid-drop by means of discharging the liquid-drop. The present invention is particularly useful as a liquid discharging device upon drying process of various liquid raw materials which are required for stable liquid discharges, and is preferable as a discharging device for various liquid, such as a liquid discharging device upon drying a solution including product aiming at supplying reactive raw materials such as pharmaceutical synthesis and powder production.
2. Description of the Prior Art
As for a conventional method of driving a liquid-drop spraying device, in a driving device for a liquid-drop spraying device comprising a plurality of minimal liquid-drop discharge units having respectively pressure means for discharging a liquid, a pressurized room for pressurizing discharge liquid, a nozzle for liquid discharge connected to the pressurized room, an inlet hole for supplying a liquid into the pressurized room, the foregoing inlet holes for supplying liquid of a plurality of liquid drop discharge units adjacent to each other being connected through a common liquid supplying path, and having the relevant piezoelectric electrostriction element in a portion of a wall portion of the relevant liquid pressurized room, there has been a conventional method of driving a liquid-drop spraying device, in which the wall portion of the relevant liquid pressurized room is deformed by applying a predetermined voltage signal (charging or discharging) to the relevant piezoelectric electrostriction element, hence, a liquid supplied to the relevant liquid pressurized room is sprayed from the foregoing nozzle by the pressure produced in the relevant liquid pressurized room, and a liquid is supplied from the inlet hole to the pressurized room by recovering the distortion of the relevant liquid pressurized room to the original form.
Then, depending upon a kind of liquid drop processing device mounted on a liquid drop spraying device, there is a device for use in supplying a large amount of liquid, a large amount of liquid is supplied by enlarging aperture of a nozzle hole and inlet hole.
However, in the case where an aperture of a nozzle hole is made too large, discharging liquid cannot be a minimal liquid-drop. Neither, as for an inlet hole, since an inlet hole not only has a function as a path through which the liquid is supplied into the pressurized room, but also has a function preventing back flow even if pressurized at the time when a liquid is sprayed from nozzle hole, the aperture of the hole cannot be widened to unlimited. Therefore, although the number of times of application per unit time period is increased and an amount of supplying volume of liquid is increased by shortening an interval time period of applying a predetermined voltage signal to piezoelectric electrostriction element, since liquid supply from an inlet hole to a pressurized room is delayed, it cannot be carried out to stably supply a larger amount of the liquid.
As for a method of driving a liquid-drop spraying device according to the present invention, in a liquid-drop spraying device comprising a plurality of minimal liquid-drop discharge units respectively having a nozzle for liquid discharge, a pressurized room for pressurizing a liquid made discharge from the relevant nozzle, an inlet hole supplying a liquid into the relevant pressurized room and piezoelectric electrostriction element making the relevant pressurized room pressurize and operate, the foregoing liquid inlet holes of a plurality of liquid-drop discharge units being connected to a common liquid supplying path, a method of driving a liquid-drop spraying device according to the present invention is provided, in which a wall portion of the foregoing pressurized room is deformed by repeatedly applying a predetermined voltage signal to the foregoing piezoelectric electrostriction element, thereby spraying a liquid supplied into the relevant pressurized room from the foregoing nozzle by the pressure produced in the pressurized room, characterized in that the ratio of the foregoing inlet hole aperture to the foregoing nozzle hole aperture (inlet hole aperture/nozzle hole aperture) ranges from equal to or more than 0.6 to equal to or less than 1.6, and the ratio of the nozzle hole aperture and the nozzle thickness (nozzle hole aperture/nozzle thickness) ranges from equal to or more than 0.2 to equal to or less than 4, after the foregoing applying voltage signal supplies and charges the current from starting charge voltage to the foregoing piezoelectric electrostriction element, retaining final charge voltage during certain time period, and then discharges having more than 2 kinds of discharge time constants are in turn performed, and the initial first discharge time constant is larger than the next second discharge time constant, making the foregoing starting charge voltage as a reference, the second discharge is started with voltage ranges from equal to or more than 35% to equal to or less than 70% of voltage difference between the foregoing starting charge voltage and the foregoing final charge voltage.
The present invention effectively acts when discharging on a liquid having a low viscosity, concretely, a liquid having a viscosity of 0.2 mPa/S-30 mPaxc2x7S, preferably a liquid having a viscosity of 0.5 mPa/S-1.2 mPa/S, in the case where liquid-drops are discharged from a plurality of liquid-drop discharge units at the same time according to the above described constitution, when a liquid is supplied from a liquid inlet hole into a liquid pressurized room after liquid discharge, since it performs rapidly suctioning the liquid having started to move than at the first suction speed and smoothly supplying the liquid and in a short time into the liquid pressurized room after first comparatively slowly suctioning the liquid and flowing the liquid into the whole inlet holes, a stable discharge of liquid can be carried out without producing bubbles in the liquid of the liquid pressurized room as well as an amount of liquid supplying per unit time period is increased.
Moreover, rapid pressure variation within pressurized room is avoided by retaining final charge voltage during certain time period immediately after discharging liquid-drop and that bubbles entering into a pressurized room from a nozzle by vibration of liquid level in a nozzle for liquid discharge is avoided, but immediately after starting discharge voltage, liquid vibration in a nozzle for liquid discharge is still remained. Hence, during the foregoing vibration is remained, discharge time constant is made larger, then suctioning the liquid by slow pressure variation, consequently when the foregoing vibration has been attenuated, if discharge is rapidly performed at the second discharge time constant, entrainment of bubbles from the nozzle for liquid discharge into the pressurized room by pressure variation of discharge time can be prevented, time interval of applying a predetermined voltage signal can be shortened to piezoelectric electrostriction element and an amount of liquid supply can be increased since discharge at the second discharge time constant is rapidly performed.
Furthermore, voltage starting discharge at the second discharge time constant is preferably made ranged from equal to or more than 35% to equal to or less than 70% of voltage difference between starting charge voltage and final charge voltage, making starting discharge voltage as a reference.
When the starting discharge voltage is equal to or less than 35%, since discharge whose discharge time constant is large, i.e., suction which is slowly performed occupies most of all suctioning steps, suction itself is securely performed, however, an amount of suction per unit time period is not taken large, since a discharge period cannot be shortened as a result, a large amount of discharge cannot be secured. Moreover, in the case where suction time is taken comparatively smaller in the situations of the range of the first discharge time constant being larger than that of the second discharge time constant so as to take a larger amount of suction per unit time period, the starting of suction is unstable, and incomplete discharge will be occurred. Furthermore, when the second starting discharge voltage is equal to or more than 70%, since discharge whose discharge time constant is large, i.e., the rate of slow suction is too small, starting of liquid suction cannot be rapidly performed, an amount of suction of liquid from the liquid inlet hole to the liquid pressurized room is decreased, entrainment of bubbles from the nozzle for liquid discharge will be occurred and spraying will be unstable.
Moreover, upon discharging in the foregoing drive waveform, in the case where the ratio of the supplying hole aperture to the nozzle hole aperture (inlet hole aperture/nozzle hole aperture) is larger, if the suction is considered, it will be well-directed, however, since the rate of the pressure upon discharge being escaped to the side of inlet hole aperture is large, discharge power will be insufficient. Moreover, in the case where it is smaller, since an amount of insufficient supply with respect to an amount of discharge is occurred, the ratio of the inlet hole aperture to the nozzle hole aperture (inlet hole aperture/nozzle hole aperture) is preferably between 0.6 and 1.6.
Furthermore, the ratio of the nozzle hole aperture to nozzle thickness (nozzle hole aperture/nozzle thickness) preferably ranges from equal to or more than 0.2 to equal to or less than 4, in the case where the ratio of the nozzle hole aperture to the nozzle thickness (nozzle hole aperture/nozzle thickness) is equal to or less than 4, residual vibration of liquid level immediately after liquid discharge can be rapidly converged by contact resistance with fluid on the wall of discharge hole, furthermore, an invasion of bubbles into the pressurized room by pressure variation within pressurized room upon discharge can be prevented, spraying stability can be enhanced, the liquid can be discharged in a shorter time period as a result, and an amount of spraying can be increased.
Moreover, in the case where the ratio of the nozzle hole aperture to nozzle thickness (nozzle hole aperture/nozzle thickness) is equal to or more than 0.2, since the contact resistance with the fluid on the wall of discharge hole is large, the occurrence of incomplete discharge due to the insufficiency of discharge force is prevented. Furthermore, when three of the foregoing ratio of the inlet hole aperture to the nozzle hole aperture, the foregoing ratio of the nozzle hole aperture to the nozzle thickness and the foregoing voltage of the second starting discharge has been fulfilled simultaneously, incomplete spraying due to an invasion of bubbles is prevented, and a large amount of spraying could have been secured.
Moreover, it is preferable that in the above described constitution, a time ranging from the time when piezoelectric electrostriction element has started discharge with the second discharge time constant to the time when the next predetermined voltage signal is applied (T4), is made ranged from equal to or more than one fourth to equal to or less than 20 fold of specific vibration period (T) at the time when a liquid is supplied to the channel path within the structure constituted of a nozzle for liquid discharge, a pressurized room for pressurizing a liquid to discharge it from the relevant nozzle, an inlet hole for supplying a liquid into the relevant pressurized room and a piezoelectric electrostriction element for making the relevant pressurized room pressurize and operate, and the ratio (T3/T4) of a time discharging at the first discharge time constant (T3) to the time ranging from the time when discharge has been started at the second discharge time constant to the time when the next predetermined voltage signal is applied to the piezoelectric electrostriction element (T4) is made ranged from equal to or more than 0.1 to equal to or less than 20 fold.
In the case where the time ranging from the time when the piezoelectric electrostriction element has started discharge at the second discharge time constant to the time when the next predetermined voltage signal is applied (T4) is equal to or less than one fourth of the specific vibration period (T), since suction speed of a liquid from a liquid inlet hole into the liquid pressurized room after liquid discharge is too high, even if the first discharge has started without discrepancy, the liquid supply from the inlet hole is insufficient in time at the time of suction during the second discharge, an invasion of bubbles from the nozzle hole for the liquid discharge into the pressurized room makes it incomplete spraying. Moreover, in the case where the above described T4 is equal to or more than 20 fold of T, since an amount of suction per unit time period is not taken large, discharge period cannot be shortened as a result and a large amount of discharge cannot be secured.
Furthermore, in the case where the ratio of the time discharging at the first discharge time constant (T3) to the time ranging from the time when discharge has been started at the second time constant to the time when the next predetermined voltage signal is applied to the piezoelectric electrostriction element (T4) is equal to or less than 0.1, since the rate of the first discharge which has a large time constant is small, the ratio of an amount of suction of the liquid during the first discharge with respect to the whole amount of suction is decreased, suction cannot be sufficient at the time of suction during the second discharge and the invasion of bubbles from the nozzle hole for the liquid discharge into the pressurized room may make it incomplete spraying. Moreover, in the case where the above described ratio is equal to or more than 20, since an amount of suction per unit time period is not taken large, discharge period cannot be shortened as a result, and a large amount of discharge cannot be secured.
Moreover, in a form of spraying a liquid-drop during discharge of the foregoing piezoelectric electrostriction element, the present invention is a method of driving a liquid-drop spraying device in which a wall portion of a pressurized room is deformed by applying different voltage signals repeatedly to the piezoelectric electrostriction element to which a predetermined voltage signal has been applied, thereby the liquid supplied into the relevant pressurized room is sprayed from the foregoing nozzle by a pressure produced in the pressurized room, characterized in that the ratio of the foregoing inlet hole aperture to the foregoing nozzle hole aperture (inlet hole aperture/nozzle hole aperture) ranges from equal to or more than 0.6 to equal to or less than 1.6, and the ratio of the nozzle hole aperture to the nozzle thickness (nozzle hole aperture/nozzle thickness) ranges from equal to or more than 0.2 to equal to or less than 4, after the foregoing different applying voltage signal has discharged the current from the foregoing piezoelectric electrostriction element to which the starting discharge voltage has been applied, the final discharge voltage during certain time period is retained, consequently, in turn, charges having equal to or more than two kinds of charge time constants are performed, and the starting first charge time constant is larger than the next second charge time constant, the second charge is started with the voltage ranging from equal to or more than 30% to equal to or less than 65% of the voltage difference between the foregoing final discharge voltage and the foregoing starting discharge voltage, and making the foregoing final discharge voltage as a reference.
In the case where liquid-drops are discharged simultaneously from a plurality of liquid-drop discharge units according to the above described constitution, when the liquid is supplied from the liquid inlet hole into the liquid pressurized room following liquid discharge, since after the liquid is first comparatively slowly suctioned and the liquid is flowed into the whole inlet holes, the liquid having started to move is suctioned rapidly than at the first suction speed and the liquid supply is performed smoothly and in a shorter time into the liquid pressurized room, a stable liquid discharge can be performed without making production of any air bubble in the liquid of the liquid pressurized room as well as an amount of the liquid supply per unit time period is increased.
Moreover, although immediately after liquid-drop discharge, abrupt pressure variation within the pressurized room is avoided by retaining final discharge voltage during certain time period, and entering of bubbles from the nozzle into the pressurized room due to the vibration of the liquid level in the nozzle for a liquid discharge is avoided, immediately after starting charge, the vibration of the liquid level in the nozzle for the liquid discharge remains. Therefore, during the foregoing vibration remains, the charge time constant is made large, the liquid is suctioned with slow pressure variation, consequently, when the foregoing vibration has been attenuated, if charge is rapidly performed with the second charge time constant, the entrainment of bubbles from the nozzle for the liquid discharge into the pressurized room due to the pressure variation during charge can be prevented, and since charge with the second charge time constant is rapidly performed, a time interval for applying a predetermined voltage signal to the piezoelectric electrostriction element can be shortened and an amount of liquid supply can be increased.
Furthermore, it is preferable that the voltage starting charge with the second charge time constant is made ranged from equal to or more than 30% to equal to or less than 65% of the voltage difference between the final discharge voltage and the starting discharge voltage, making the final discharge voltage as a reference.
In the case where the starting charge voltage is equal to or more than 65%, although the discharge whose discharge time constant is large, i.e., the suction which is slowly performed occupies most of all suction steps, the suction itself is securely performed, since an amount of suction per unit time period is not taken large, discharge period cannot be shortened as a result, a large amount of discharge cannot be secured. Moreover, if the suction time is taken comparatively smaller in the situations of the range of the first charge time constant being larger than that of the second charge time constant so as to take a larger amount of suction per unit time period, the starting of suction will be unstable and incomplete discharge will be occurred. Moreover, in the case where it is equal to or less than 30%, since the rate of the charge whose charge time constant is large, i.e., the suction which is slowly performed is too small, the starting of suction of the liquid cannot be rapidly performed, an amount of suction from the liquid inlet hole into the pressurized room following liquid discharge is decreased, and spraying is unstable because the entrainment of bubbles from the nozzle for the liquid discharge occurs.
Moreover, in the case where discharge is performed in the above described drive waveform, if the ratio of the supplying hole aperture to the nozzle hole aperture (inlet hole aperture/nozzle hole aperture) is larger, it will be lead to a good direction in the consideration of suction, however, since the rate of the pressure at the discharge being escaped to the side of inlet hole, discharge force will be insufficient. Moreover, in the case where the ratio is smaller, since the insufficiency of an amount of supply with respect to an amount of discharge is occurred, it is preferable that the ratio of the inlet hole aperture to the nozzle hole aperture (inlet hole aperture/nozzle hole aperture) ranges from equal to or more than 0.6 to equal to or less than 1.6.
Furthermore, it is preferable that the ratio of the nozzle hole aperture to the nozzle thickness (nozzle hole aperture/nozzle thickness) ranges from equal to or more than 0.2 to equal to less than 4, in the case where the ratio of the nozzle hole aperture to the nozzle thickness (nozzle aperture/nozzle thickness) is equal to or less than 4, residual vibration of the liquid level immediately after liquid discharge can be rapidly converged by the contact resistance with the fluid on the wall face of discharge hole, furthermore, the invasion of bubbles into the pressurized room due to the pressure variation within the pressurized room during charge can be prevented, the spraying stability can be enhanced, discharge can be performed in a shorter time period as a result, and an amount of spraying can be increased. Moreover, in the case where the ratio of the nozzle hole aperture to the nozzle thickness (nozzle hole aperture/nozzle thickness) is equal to or more than 0.2, since the contact resistance with the fluid on the wall face of the discharge hole is large, the occurrence of incomplete discharge due to the insufficiency of the discharge force can be prevented.
Furthermore, when the three of the above described ratio of inlet hole aperture to the nozzle hole aperture, the ratio of the nozzle hole aperture to the nozzle thickness and the second starting charge voltage have been fulfilled simultaneously, incomplete spraying due to the invasion of bubbles can be prevented and a large amount of spraying can be secured.
Moreover, it is preferable that in the above described constitution, a time ranging from the time when piezoelectric electrostriction element has started discharge at the second discharge time constant to the time when the next predetermined voltage signal is applied (T40), is made ranged from equal to or more than one fourth of T to equal to or less than 20 T of specific vibration period (T) at the time when a liquid is supplied to the channel path within the structure constituted of a nozzle for liquid discharge, a pressurized room for pressurizing a liquid to discharge from the relevant nozzle, an inlet hole supplying a liquid into the relevant pressurized room and a piezoelectric electrostriction element for making the relevant pressurized room pressurize and operate, and the ratio (T30/T40) of a time for discharging at the first discharge time constant (T30) to the time ranging from the time when discharge has been started at the second discharge time constant to the time when the next predetermined voltage signal is applied to the piezoelectric electrostriction element (T40) is made ranged from equal to or more than 0.1 to equal to or less than 20.
In the case where the time ranging from the time when the piezoelectric electrostriction element has started discharge at the second discharge time constant to the time when the next predetermined voltage signal is applied (T40) is equal to or less than one fourth of the specific vibration period (T), since suction speed of a liquid from a liquid inlet hole into the liquid pressurized room after liquid discharge is too high, even if the first discharge has started without discrepancy, the liquid supply from the inlet hole is insufficient in time at the time of suction during the second discharge, an invasion of bubbles from the nozzle hole for the liquid discharge into the pressurized room makes it incomplete spraying. Moreover, in the case where the above described T40 is equal to or more than 20 fold of T, since an amount of suction per unit time is not taken large, discharge period cannot be shortened as a result and a large amount of discharge cannot be secured.
Furthermore, in the case where the ratio of the time for discharging with the first discharge time constant (T30) to the time ranging from the time when discharge has been started at the second time constant to the time when the next predetermined voltage signal is applied to the piezoelectric electrostriction element (T40) is equal to or less than 0.1, since the rate of the first discharge which has a large time constant is small, the ratio of an amount of suction of the liquid during the first discharge to the whole amount of suction is decreased, suction cannot be sufficient at the time of suction during the second discharge and the invasion of bubbles from the nozzle hole for the liquid discharge into the pressurized room may make it incomplete spraying. Moreover, in the case where the above described ratio is equal to or more than 20, since an amount of suction per unit time period is not taken large, discharge period cannot be shortened as a result, and a large amount of discharge cannot be secured.